The present invention is related to a filtering apparatus. More particularly this invention concerns a seal arrangement for a filtering apparatus.
Filtering devices are known such as described in U.S. Pat. Nos. 3,107,217 and 3,190,449 as well as the references cited therein which have a closed housing in which is provided a plurality of filter elements carried on a hollow shaft. The filter elements each have one or more liquid-pervious faces so that when pressure is applied to the interior of the hollow shaft liquid or gas is pumped into this shaft through these filter surfaces, thereby being filtered and leaving any suspended particles behind. In such devices it is common practice to rinse off the filter cake between filtering cycles by rotating the hollow shaft and simultaneously squirting liquid on the filter elements, as described in the commonly owned patent application Ser. No. 694,196 filed June 9, 1976.
So long as such devices are used at every-day temperatures with water or the like there is little difficulty in sealing the interior of the hollow shaft relative to the compartment defined between the housing and the outside of the hollow shaft. When, however, highly corrosive or active liquids are being filtered, or when extremely high temperatures are employed, it becomes a very difficult matter adequately to seal between this compartment inside the shaft and the compartment outside the shaft. It is absolutely essential in such filtering devices, particularly when used with liquefied coal or the like, that none of the unfiltered liquid be able to leak past the filter elements and mix with the filtrate. Furthermore this problem is complicated in some systems which must maintain a proper seal between the shaft compartment and the housing compartment during relative rotation of the shaft and the housing. In such systems it is impossible to use customary seals with corrosive or very hot liquids, or when very high pressures, above 20 bar, are employed.
Various other prior-art filter apparatus can be seen in Swiss Pat. No. 400,688; Swiss patent application No. 7960/75 and German utility model No. 7,435,463.